Light sources to generate white or coloured light are well known. Typically, a light source is defined by its light output in lumens or Watts, and other features such as those parameters that may be derived from the light spectrum such as e.g. the colour coordinates in a given colour space, the correlated colour temperature (CCT), the colour rendering index (CRI), the gamut area index (GAI), etc.
In recent days more indicators are appearing that account for the interaction between the spectral power distribution (or spectrum) of a light source and different biological systems, such as the human brain, plants or other animals. All these applications, each of them with their own indicators, highlight the importance that a control over the spectral power distribution of the light has in professional environments where the properties of light have to be carefully controlled.
In order to be able to shape the spectral power distribution, the light source that produces the light output may require being composed of individually addressable wavelength light channels and a control unit for calculating the weights (or adjustments) to be provided to every light channel to obtain the target spectrum.
A light channel may be defined herein as a light production unit which is independently (individually) addressable (controllable) by the controller. A light channel may be constituted by one or more light emitters according to the light emission characteristics of said light emitters; i.e. light emitters with substantially homogeneous light emission properties may form a particular light channel. A lighting device may have an arbitrary number of light emitters and corresponding light channels.
Several control methods can be found in the background art that aim at having a well-defined spectral power distribution.
In an example, a target spectrum is matched using a luminaire having a plurality of known LEDs (their spectrum characteristics are known), by theoretically estimating the contribution (coefficient or weight) of each LED. The method further describes calculating the CIE chromaticity coordinates of the target spectrum and calculating the CIE coordinates of the LED luminaire light spectrum and fine-adjusting the contribution of each LED to minimize the chromaticity error. This seems to describe an optimization based on calculations that take into account pre-known features of the LEDs. A drawback of this approach is that either temperature changes or the aging of the LEDs may cause a loss of knowledge of the pre-known features of the LEDs, so that the reproduction of the target spectrum may be less accurate over time.
In another example, described is another LED luminaire having a plurality of LEDs capable of reproducing a target spectrum. The optimization of the emitted spectrum vs. target spectrum is performed using spectrometer data, which necessarily comes from a spectrometer. This device may thus result expensive due to the cost of spectrometers.
In a further example, described is a luminaire capable of reproducing a desired target spectral power distribution using a plurality of LEDs. An optical measurement device is used to measure emitted light, the optical measurement device being able to measure the emitted spectrum and is a spectrometer or a plurality of colour optical sensor matching the light emitters of the luminaire. This device may thus also be relatively expensive.
An object of the present disclosure is improving the prior methods, computer programs and controllers (systems) for controlling lighting devices to produce illumination based on a reference spectral power distribution.